It is known to ascertain the thermal loading of the starting motor (abbreviated as starter) by measuring the armature current or the temperature of the carbon brushes, using appropriate sensors. However, the known devices have the disadvantage of being relatively costly, since additional sensors are needed. For example, an appropriate temperature sensor is needed to measure temperature, the sensor having to be in proximity to the carbon brushes, in order that it can essentially detect their temperature. The known methods for measuring current also require a measuring element, e.g. a shunt in the measuring line or, in the case of a contactless measurement, e.g. a Hall sensor. Both methods exact costs for the sensors, wiring, as well as their installation, and are an additional risk to the reliability of the starting motor. Furthermore, a circuit arrangement for electric starting motors is known from German Patent No. 2700982, which evaluates the time-related current variations or voltage variations of the current supplied to the starting motor. If the variation over time falls below a predefined threshold value, this is interpreted as sustained operation of the internal combustion engine, and the starting motor switches off, since the voltage variations are smaller during sustained engine operation than during starting.
The starting motor of the present invention has the advantage of the installation not requiring additional hardware such as sensors, wiring, possibility for control, etc., since these functions can be implemented by the components already present in the control circuit. It is considered to be especially advantageous that, from the measurement of the voltage ripple, e.g. by simulation or empirical measurement, one can easily derive local temperature peaks, e.g. at the carbon brushes, or derive the load of the starting motor. In certain operational situations, such as xe2x80x9ccrankingxe2x80x9d for a long time after a cold winter night, or running by means of the starter, without the support of the motor, while a ship is being loaded (because the tank is empty), the starter can experience overloading which would result in it being damaged or destroyed. This is advantageously prevented by the subject matter of the present invention.
It is particularly advantageous that the induction flux to the internal combustion engine is immediately interrupted by switching off the primary current, and therefore, the starting motor cannot be heated any further. The starting motor can then only be used again after it cools off, in order to prevent it from being damaged.
It is also favorable that the armature current of the starting motor can be ascertained indirectly from the data already existing for a corresponding reference starter. It is often necessary to determine the armature current, since the temperature of the starting motor carbon brushes can be ascertained, using this value. A high armature current results in a correspondingly high temperature, due to the heating of the starting motor, as well as the heating of the sparking brush, while the temperature is lower at a lower armature current.
A further advantage is that, for purposes of control, the measured voltage-ripple values can be read off at a corresponding output. For purposes of servicing, this simplifies the discovery of a possible error source. Errors can then be read out during the next maintenance inspection of a motor vehicle.
Since the control circuit is normally equipped with a small microcomputer chip, the existing control circuit can be advantageously expanded, using a corresponding, supplementary software program as a control program for the starting motor. The improvement of the control-circuit reliability is also particularly advantageous, since the unneeded components mean that no risk of error can arise. Furthermore, every type of starting motor can easily be accommodated by a simple modification of the control program.
It is also regarded as an advantage that the limiting load for the starting motor can be appropriately adjusted by taking the ambient temperature into account. For example, the limiting value can be correspondingly reduced at a high ambient temperature since, in this case, it is possible for damage to occur earlier.